One of my worst school memories is about the pledge. We had a substitute teacher one day in first grade. One of the boys was goofing off during the pledge, and the sub screamed at him while yanking him by the arm about how her husband fought for this country and no smart alecky kid was going to diminish his contribution, etc. She had him in tears and made him say it over and over until he would do it without crying. Then she sent him to the office. Yikes.
Also, I remember we had two kids who were Jehovah's Witnesses who went into the hall while we said the pledge, also starting in first grade. Everyone treated them like they were freaks. I wonder at what age do they get that they are making a choice to participate or not for this or that reason and at what point are they either doing it just to avoid ridicule or doing it/not doing because of mom and dad's preferences.
Unfortunately, where I live, differences will only get your butt kicked at recess. No one is shy about professing his or her intolerance. If you don't say 'under God', you must be evil. If you don't say it at all, you can count on getting pummeled.